netdev - Re: [PATCH net-next] tcp: TCP_NOSENT

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Date:	Mon, 22 Jul 2013 19:32:43 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH net-next] tcp: TCP_NOSENT_LOWAT socket option

On Mon, 2013-07-22 at 17:40 -0700, Eric Dumazet wrote:
> On Mon, 2013-07-22 at 17:13 -0700, Eric Dumazet wrote:
> 
> > 
> >  Performance counter stats for './netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c':
> > 
> >            714,395 context-switches                                            
> 
> Hmm, actually I need to send a v3, because sk_stream_write_space() is
> waking sockets too often.
> 

Yep, new results are more the expected ones :

lpq83:~# echo -1 >/proc/sys/net/ipv4/tcp_notsent_lowat
lpq83:~# perf stat -e context-switches ./netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c
TCP SENDFILE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.17.84 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % U      us/KB   us/KB

 87380  16384  16384    20.00      9408.18   1.60     -1.00    0.333   -1.000 

 Performance counter stats for './netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c':

            49,543 context-switches                                            

      20.005432791 seconds time elapsed

lpq83:~# echo 131072 >/proc/sys/net/ipv4/tcp_notsent_lowat
lpq83:~# perf stat -e context-switches ./netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c
TCP SENDFILE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.17.84 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % U      us/KB   us/KB

 87380  16384  16384    20.00      9407.71   1.55     -1.00    0.323   -1.000 

 Performance counter stats for './netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c':

           345,670 context-switches                                            

      20.004435166 seconds time elapsed

And the receiver disables LRO/GRO, no real difference this time :

lpq83:~# perf stat -e context-switches ./netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c
TCP SENDFILE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.17.84 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % U      us/KB   us/KB

 87380  16384  16384    20.00      9382.90   2.14     -1.00    0.448   -1.000 

 Performance counter stats for './netperf -H 10.246.17.84 -l 20 -t TCP_SENDFILE -c':

           336,501 context-switches                                            

      20.004579650 seconds time elapsed

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